Data network services often utilize multiple data links. An Internet service provider, for example, may connect a subscriber to the Internet using multiple optical fibers where each of the fibers relays information between the provider and the subscriber.
In some cases, providers use multiple data links so that if a link fails, such as because a road construction crew severs one of the fibers connecting the provider and the subscriber, the subscriber will still have access to the data network. If only one link connected the subscriber to the provider and it was cut, the subscriber would lose access.
In some other cases, providers use multiple data links because one link is too slow to provide a subscriber's desired communication rate. A 100-megabit-per-second (Mbps) Ethernet link, for example, can transmit and receive data at a rate of up to, but not greater than, 100 Mbps. If a subscriber requires more than 100 Mbps, the provider may provision a second link. These two links—while separate physically—can be grouped. This group then has a physical maximum data rate of 200 Mbps (100 Mbps plus 100 Mbps).
The group of links may also have a permitted data rate, which is often based on the subscriber's needs or the provider's capabilities. This permitted data rate for the group (and thus the subscriber) may be less than the group's physical maximum data rate. For example, a provider may create a group having two 100 Mbps links with a physical maximum rate of 200 Mbps and assign a permitted data rate of 150 Mbps to the group. Often the service provider's equipment (e.g., switch or router) enforces the permitted data rate assigned to a group. This equipment may reject data packets sourced at a rate in excess of the permitted data rate.
Currently, this equipment often enforces this permitted data rate by allocating a maximum rate for each physical link belonging to the group. The equipment sets this per-link maximum rate as the subscriber's permitted data rate divided by the number of active physical links in the subscriber's group. For example, if a group has two 100 Mbps physical links, and the permitted data rate assigned to the group is 150 Mbps, the equipment at one end permits the remote equipment to transmit data packets on each of the two physical links at a rate of no more than 75 Mbps. Thus, if the remote equipment transmits data on either of the two physical links at a rate in excess of 75 Mbps, the local equipment may drop a subset of the data packets received on that link.
If one of the links in the group fails or the remote equipment transmits more than the per-link maximum rate on one link but less than the per-link maximum rate on another, the local equipment may prevent the remote equipment from using as much of the permitted rate as possible. If one of the two 100 Mbps links of the above-mentioned group fails, the subscriber will only be able to transmit data at 75 Mbps. If the remote equipment attempts to transmit 90 Mbps on the only available physical link of the group, the local equipment may drop 15 Mbps because that physical link has exceeded its allocated 75 Mbps per-link maximum rate. This 15 Mbps is dropped despite the fact that the remote equipment has not exceeded its permitted data rate of 150 Mbps and the group of links still has a physical maximum data rate of 100 Mbps.
Or, if neither of the physical links fails but the remote equipment attempts to transmit 100 Mbps on one link and only 50 Mbps on the other, the local equipment may only permit the subscriber to transmit data at 125 Mbps. In this case the local equipment drops 25 Mbps of the data packets received on a first physical link for exceeding the physical link's allocated portion —75 Mbps—even though the subscriber has not exceeded its permitted data rate of 150 Mbps.